Alternator and method of manufacture

ABSTRACT

An alternator has a molded plastic, electrically conductive D.E. frame in which a sealed bearing is molded in place with the formation of the D.E. frame  14 . When the D.E. frame is removed from its plastics injection mold and while the frame is still hot, the stator is installed in the D.E. frame and the frame allowed to cool and constrict about the stator. The companion S.R.E. frame is preferably fabricated of non-conductive plastics material.

This application division of U.S. continuation application Ser. No.10/794,908, filed Mar. 5, 2004 which claims priority to U.S. applicationSer. No. 10/098,782, filed Mar. 14, 2002 which claims priority to U.S.provisional patent application Ser. No. 60/276,723, filed Mar. 16, 2001.

TECHNICAL FIELD

This invention relates generally to alternators for internal combustionengine applications and the like and to methods of manufacturing suchalternators, and further to the manufacture of molded plastic housingsfor electrical devices generally having a bearing for supporting arotating shaft.

RELATED ART

Alternators, particularly those for automotive engine applications, arefabricated with drive-end (D.E.) and a stator-regulator-end (S.R.E.)frames which house a stator and rotor and support the other componentsthat make up the alternator. The stator is normally fitted in the D.E.frame. Both frames are typically cast from aluminum and have severalsurfaces that require secondary machining to prepare the surfaces tosupport a corresponding component of the alternator. One of thosesurfaces is the stator bore of the D.E. frame which supports the stator.Once machined, the D.E. frame is heated to expand the stator bore atwhich point the stator is inserted into the D.E. frame and the framethen cooled to shrink the D.E. frame about the stator to retain thestator in place. The machining and heating operations add to the cost ofmanufacturing such alternators.

Aluminum is typically employed for the D.E. frame for its ability toprovide a ground path for the stator and for its strength anddimensional stability at elevated operating temperatures of the stator.

Included among the other machined surfaces of such aluminum D.E. framesis a bearing well whose inner surface is machined to receive a sealedD.E. roller bearing with a press fit. The well includes a lip ofaluminum material extending about the opening of the bearing well which,after installation of the bearing, is spun over onto the outer race tocapture the bearing axially within the well. The secondary machining andlip deformation operations further add to the cost of alternators.

Moreover, when it is desired to rebuild a spent alternator, thespun-over lip must be ground off and the D.E. frame modified with aretro-fit metal retainer fastened to the bearing well in position of theformer spun-overlip. Such process involves remachining of the bearingwell wall, removal of the spun-overlip and machining of the frame toreceive the retainer ring, and the provision and fastening of theretainer ring to make use of the otherwise spent, aluminum D.E. frame.Such adds cost to the rebuilding of spent alternators.

Other surfaces that require machining are the mating surfaces of theD.E. and S.R.E. frames, which are brought together and then secured byfasteners. Also machined are several bores which are fitted with pressedsteel bushings for mounting the alternator in service. Such dissimilarmetal materials (i.e., steel against aluminum) present issues ofcorrosion which must be contended with.

U.S. Pat. No. 4,705,983 discloses an alternator having, as part of itsstructure, an end shield fabricated of insulating plastics material andformed with a central molded hub that, after forming, is provided toseat a roller bearing.

U.S. Pat. No. 5,982,057 discloses molding a plastics housing in placeabout a stator of an electric motor along with a molded-in bearing bush.Following molding, a roller bearing is installed in the bearing bush.Provision of the molded-in bearing bush adds cost and complexity to thestructure.

It is an object of the invention to overcome or greatly minimize theforegoing limitations in connection with alternators and otherelectrical devices employing a plastic housing to support a bearing ofthe art.

SUMMARY OF THE INVENTION AND ADVANTAGES

According to one aspect of the invention, an alternator is providedcomprising a D.E. frame having an electrical grounding portion; a statorsecured to the D.E. frame remote from the grounding portion; a D.E.bearing secured to the D.E. frame; a S.R.E. frame secured to the D.E.frame, a S.R.E. bearing secured to the S.R.E. frame, a rotor housedwithin the D.E. and S.R.E. frames and journaled by the D.E. and S.R.E.bearings for rotation relative to the rotor, and wherein the D.E. frameis fabricated of plastics material and includes an electricallyconductive ground circuit coupling the stator electrically to the groundportion. This aspect of the invention has the advantage of providing aplastics D.E. housing which is less costly and lighter weight than thealuminum counterparts and yet is provided with a ground path for thestator.

According to a further aspect of the invention, a housing assembly, suchas the D.E. or S.R.E. frame of an alternator, includes a sealed rollerbearing having inner and outer races and roller elements therebetween,and a molded plastics housing having a bearing well within which thesealed roller bearing is molded in place. The bearing well includes aninner wall surface engaging an outer surface of the outer race, andaxial restraining portions which extend radially inwardly from the innerwall of the well in overlying relation to axially opposite end faces ofthe outer face for restraining the bearing axially against removal fromthe bearing well. According to a related method of the invention, duringmolding, the bearing is maintained at a temperature in the mold belowthat which would cause heat damage to the bearing.

This aspect of the invention has the advantage of providing a simple,effective way of securing a sealed, heat-sensitive roller bearing withina housing, such as an alternator frame, which avoids machining orpressing operations or provision of a premolded bearing bush. The sametechnique and features are applicable to other plastics housings ofelectrical devices in which the bearing is molded in place in thehousing.

According to yet another aspect of the invention, an alternator isformed according to a method in which the D.E. frame is molded fromplastics material and is removed from the mold. While still hot, thestator is installed in the D.E. frame and the plastics material allowedto cool to constrict about the stator to secure the stator in place inthe D.E. frame.

According to still a further aspect of the invention, a ground path ismolded in place in a plastic housing of an electrical component toestablish a defined electrical path through the plastics housing.

THE DRAWINGS

A presently preferred embodiment of the invention is disclosed in thefollowing description and in the accompanying drawings, wherein:

FIG. 1 is an exploded perspective view of an alternator constructedaccording to a presently preferred embodiment of the invention;

FIG. 2 is an enlarged elevation view looking into the D.E. frame;

FIG. 3 is an enlarged, exploded perspective view of the D.E. frame andstator prior to their assembly;

FIG. 4 is a view like FIG. 3 following assembly of the stator in theD.E. frame;

FIG. 5 is an enlarged fragmentary cross-sectional view taken generallyalong lines 5-5 of FIG. 2; and

FIG. 6 is an enlarged perspective view of a bearing whose outer race isformed with retaining grooves shown interlocked with retaining ribs ofthe housing.

DETAILED DESCRIPTION

Referring initially to FIG. 1, an exploded perspective view of analternator 10 is shown constructing according to a presently preferredembodiment of the invention. The alternator 10 includes a housingassembly 12 comprised of a drive-end (D.E.) frame 14, and astator-regulator-end (S.R.E.) frame 16 which are joined at matingflanges 18, 20 and secured by bolts 22 to house therein a stator 24 anda rotor 26.

The D.E. frame 14 is molded of plastics material and mounts a D.E.bearing 28. The S.R.E. frame 16 is likewise preferably fabricated ofplastics material and mounts a corresponding S.R.E. bearing 30. Thebearings 28, 30 are double sealed roller bearings of the typeschematically illustrated in FIG. 5 including an outer race 32, an innerrace 34 and a plurality of rolling elements, such as the illustratedbearing balls 36, captured between the outer and inner races 32, 34 toenable the inner race 34 to rotate relative to the outer race 32.Annular seals 38 span the gap between the inner and outer race toprovide a sealed environment to the roller elements 36, which arelubricated with grease 40. Such sealed roller bearings 28, 30 areheat-sensitive, in that if the bearings 28, 30 are heated above acritical upper operational limit temperature, either the seals 38overheat and fail and/or the grease 40 within the bearings 28, 30liquefies and leaks out of the bearings past the seals 38 and thebearing fails. The critical upper limit operating temperature will varydepending on the type of grease and seals employed in a given bearing,and an understanding of the operating limits are known by those ofordinary skill in the art of alternators and bearings. The bearings 28,30 surround openings in the frames 14, 16 through which a shaft of therotor 26 extends and is journaled by the bearings.

According to one aspect of the invention, at least the D.E. bearing 28is molded in-place with the formation of the D.E. frame 14 andpreferably the S.R.E. frame 16. As shown best in FIG. 5, the bearing 28is inserted in a mold (not shown) configured to form the D.E. frame 14into which hot, flowable plastics material is introduced which, asshown, flows around the bearing 28 to capture the bearing 28 within abearing well 42 of the D.E. frame 14. More specifically, the bearingwell 42 is comprised of a cylindrical hub or bearing well ball portion44 projecting axially inwardly from an end wall 46 of the D.E. frame 14.The hub 44 has an inner wall surface 48 which engages an outerperipheral surface 50 of the outer race 32. An annular retaining portionor flange 52 molded as one piece with the D.E. frame 14 projectsradially inwardly from the inner wall surface 48 on opposite axial sidesof the D.E. bearing 28 in overlying relationship to axially opposite endfaces 54, 56 and in radially outer spaced relation to the inner race 34for restraining the D.E. bearing within the bearing well 42 in bothaxial directions via upper and lower retaining portions 52, 53 andradially via the inner wall surface 48. In this way, the bearing 28 iscaptured in place during molding by the structure of the D.E. framealone. The lower retaining portion 53 forms part of the end wall 46 ofthe frame and extends from the opening 55 in the end wall 46 to thebearing well wall or hub 44.

As shown in FIG. 6, the outer surface 50 of the outer race 32 may beformed with a series of retaining grooves 58 which are recessed into theouter surface 50. During molding, the grooves 58 are filled with theplastics material of the D.E. frame 14 to provide interlocking retainingribs 60 of the D.E. frame 14. The grooves 58 and ribs 60 are preferablytransverse to the longitudinal axis and lateral plane of the outer race32, such that the interlocking grooves 58 and ribs 60 crisscross oneanother and constrain the outer race 32 against longitudinal movementalong the axis as well as rotational movement about the axis of theouter race 32. The grooves 58 may be ground into the outer surface 50 orprovided by other suitable means. The grooves preferably have a depth ofabout 0.020-0.030 inches and a width of about 0.060 inches. The sametechnique for molding in place a bearing in a plastic housing is equallyapplicable to other housing components such as electric starters and thelike.

Turning now to FIGS. 2 and 3, the D.E. frame 14 has a stator hub 62provided by an outer peripheral wall of the frame 14 formed with aninner stator bearing surface 64 which, in its as-molded state withoutmachining, is sized to engage an outer surface 66 of the stator 24 withsufficient frictional interference to secure the stator 24 within theD.E. frame 14.

According to the invention, the D.E. frame 14 is molded such that thestator bearing surface 64 has a size in relation to the outer surface 66of the stator 24 that, when the D.E. frame 14 is cooled to ambienttemperature, tightly constricts about and grips the outer surface 66 ofthe stator 24 to secure the stator 24 in place within the D.E. frame 14.According to a preferred aspect of the invention, the D.E. frame 14 ismolded initially without the stator 24. Upon solidification of theplastics material of the D.E. frame 14, but while the D.E. frame 14 isstill hot from molding, the D.E. frame 14 is removed from the mold and,while still hot, the stator 24 is inserted into the stator hub 62 of theD.E. frame 14. The temperature, of course, will vary depending upon thematerial used to form the D.E. frame 14. However, at the temperature ofremoval from the mold, the heat of the D.E. frame 14 causes the statorbearing surface 64 to be in an expanded state whereby the stator 24 canbe inserted into the stator hub 62 with very little effort due to theradial clearance between the stator 24 and stator hub 62. Onceinstalled, the D.E. frame 14 is allowed to cool, which causes the statorbearing surface 64 to constrict tightly about the outer surface 66 ofthe stator 24, securing the stator 24 both axially and rotatably againstmovement relative to the D.E. frame 14 and preventing its removal fromthe frame 14.

Preferably, the inner cylindrical stator bearing surface 64 is formedwith an alignment rib 68 which projects radially inwardly from thesurface 64. The alignment rib 68 extends axially along the surface 64 ofthe stator hub 62. The alignment rib 68 is thus fixed relative to theframe 14 and projects inwardly from the stator bearing surface 64. Theouter surface 66 of the stator 24 is formed with a plurality of axialgrooves 70, any one of which can receive the rib 68. In most cases, thestator 24 will have a preferred angular orientation relative to the D.E.frame 14. As illustrated in FIGS. 3 and 4, the stator 24 can be markedwith a visible alignment indicator 72 positioned such that when alignedwith the alignment rib 68 the stator 24 is in the proper angularorientation relative to the D.E. frame 14. As shown in FIG. 4, duringinstallation of the stator 24 when the D.E. frame 14 is still hot fromthe mold, the appropriate groove 70 associated with the alignmentindicator 72 is guided into position over the alignment rib 68 toquickly, easily and positively orient the stator 24 precisely relativeto the D.E. frame so as to eliminate variation between components.

The stator 24 preferably includes a stack of metal laminates 74 andcopper windings 76.

The D.E. frame 14 is preferably formed with at least one and, asillustrated here, a pair of electrically grounding portions 78 in theform of ears which have molded-in metal bushings or sleeves 80 defininglined bolt holes for received bolts (not shown) which mount thealternator 10 to the frame or other structure of a vehicle or the likeand provides, by that connection, a grounding vehicle. The sleeves 80are preferably aluminum.

The plastics molded D.E. frame 14 includes an electrically conductiveground circuit which couples the stator 24 electrically to the groundingportion 78. According to one aspect of the invention, the D.E. frame 14is molded from an electrically conductive plastics composite materialwhich renders the entire D.E. frame 14 conductive and thus establishingthe ground path. Suitable materials are those which can withstand theoperating temperature of an alternator while maintaining adequatestrength and stability to provide the needed support of the D.E. frame14. Among the candidate materials are high temperature, heat stabilizedpolyamide resins having a carbon fiber fill of about 35 to 50 vol %which renders the composite electrically conductive to provide theelectrically conductive path from the rotor 26 to the grounding portion78. One such material is manufactured by E.I. du Pont de Nemours(DuPont) under the Zytel® family. Alternatively, or in addition toconduction by the composite material per se, the ground path 82 may beprovided by an embedded wire 84 leading to the sleeve 80 and molded inplace during the molding of the D.E. frame 14, or an external wire 86added after molding the D.E. frame 14. The same technique for providinga molded-in ground path is applicable to housings of other electricaldevices, such as starters and the like.

According to a further aspect of the invention, the S.R.E. frame 16 isfabricated of a plastics material that is relatively non-conductive inrelation to the conductivity of the D.E. frame 14. In other words, theS.R.E. frame 16 is more insulating than electrically conductive inrelation to the properties of the D.E. frame 14. The S.R.E. frame 16 maybe fabricated of a substantially non-conductive plastics material. Asuitable material may comprise 35-50 vol % glass fiber- filled polyamideresin of the Zytel® family. Making the S.R.E. frame 16 fromnon-electrically conductive plastics material has the advantage ofinsulating many of the component parts mounted on the S.R.E. frame whichnormally require special insulating shields and the like to preventconductive between the components and the usual aluminum S.R.E. frame.Mounted on the backside of the S.R.E. frame 16 is a regulator 88, arectifier 90, and a brush holder assembly 92. When installed, thesecomponents are concealed by an end cover 94 which likewise may beplastic. With the non-conductive plastic S.R.E. frame 16, there is noneed to electrically insulate the regulator 88 and rectifier 90 from theS.R.E. frame 16, which greatly simplifies and reduces the cost ofmanufacturing alternators.

The invention further contemplates methods in remanufacturing spentalternators both of the traditional metal frame construction and thoseof the plastic frame variety of the invention. In either case, the rotorand bearing, along with any other inserts, are removed from the D.E.frame and a new D.E. frame 14 molded from the plastics material aspreviously described, preferably including the molded-end bearing 28.The spent plastic D.E. frame 14 can be ground and recycled. The stator24 is installed by the same process of inserting it into the frame 14when the frame 14 is hot out of the mold.

The disclosed embodiment is representative of a presently preferred formof the invention, but is intended to be illustrative rather thandefinitive thereof. The invention is defined in the claims.

1. A method of securing a sealed roller bearing having an inner race, anouter race and lubricated rolling elements disposed between the innerand outer races in a molded plastic housing member, comprising:inserting the sealed bearing in a mold configured to form the housingmember; introducing hot, flowable plastics material into the mold andallowing the material to flow about the outer race of the sealed bearingto fix the sealed bearing in the resultant housing member; and duringmolding, maintaining the temperature of the sealed roller bearing at atemperature below which the sealed bearing would be damaged by heat. 2.The method of claim 1 in which the outer race has an outer surface andopposite end faces, and wherein the plastics material flows about theouter surface and end faces during molding to circumferentially andaxially encapsulate the outer race.
 3. A housing assembly comprising: asealed bearing having an inner race, an outer race, and lubricatedroller elements disposed between the inner and outer races; a moldedplastics housing body having a bearing well within which said sealedroller bearing is molded in place including an inner wall surfaceengaging an outer surface of said outer race, and axial restrainingportions extending radially inwardly from said inner wall in overlyingrelation to axially opposite end faces of said outer race forrestraining said bearing axially against removal from said bearing wall.4. A housing assembly, comprising: a first housing member fabricated ofinjection molded plastics material; a second housing member joinable tosaid first housing member; said first housing member having an end wallportion and an outer peripheral side wall portion extending from saidend wall portion to provide a generally cup-shaped configuration to saidfirst housing member; a shaft opening formed in said end wall portion inradially inwardly spaced relation to said outer peripheral side wallportion; a bearing well wall portion extending from said end wallportion to an upper end in surrounding relation to said shaft opening,said bearing wall portion having an inner wall surface spaced from andconcentric with said shaft opening; an annular end flange section ofsaid end wall portion extending between said shaft opening and saidinner wall surface of said bearing well wall portion and providing,together with said bearing well portion, a cup-shaped bearing well; abearing disposed in said bearing well, said bearing having an outer raceengaging said inner wall surface of said bearing well wall portion andsaid annular end flange section of said end wall portion; and an annularretaining flange portion molded as one piece with said bearing well wallportion of said first housing member and extending radially inwardly ofsaid inner wall surface of said bearing well wall portion in overlying,confronting relation to said outer race of said bearing to retain saidbearing against removal from said bearing well.
 5. The housing assemblyof claim 4 wherein said outer race of said bearing has a generallycylindrical outer surface and includes a plurality of recesses extendinginto said outer surface, said bearing well wall portion includinginterlocking retaining projections extending into said recesses inradially inwardly projecting relation to said inner wall surface of saidbearing well wall portion.
 6. The housing assembly of claim 5 whereinsaid recesses of said outer race comprise a series of grooves disposedtransverse to a longitudinal axis of said shaft opening.
 7. The housingassembly of claim 5 wherein said recesses comprises a plurality ofcrisscrossing grooves disposed transverse to a longitudinal axis of saidshaft opening and transverse to a plane normal to said longitudinalaxis.
 8. The housing assembly of claim 7 wherein said crisscrossinggrooves intersect one another.
 9. The housing assembly of claim 7wherein said interlocking retaining projections fill said grooves. 10.The housing assembly of claim 4 wherein said bearing includes an innerrace supported for free rotation relative to said outer race.
 11. Thehousing of claim 4 wherein said bearing comprises a sealed bearing. 12.The housing assembly of claim 11 wherein said sealed bearing includes aninner race spaced from said outer race, a plurality of bearing elementsdisposed in a space between said inner and outer races, and a sealextending between said inner and outer race and sealing said space fromthe external environment.
 13. A method of making a housing assembly,comprising: fabricating a first housing member; fabricating a secondhousing member by injecting hot plastics material into a mold cavity andmolding the plastics material around an outer race of a sealed bearingto secure the outer race to the second housing member while retainingrelative rotational movement of an inner race of the bearing.
 14. Themethod of claim 13, including forming recesses in an outer surface ofthe outer race and flowing the plastics material into the recessesduring molding.
 15. The method of claim 14 wherein the recesses areformed by forming a series of crisscrossing grooves in the outer surfaceand filling such grooves with the plastics material during molding. 16.The method of claim 13 including molding the plastics material aroundopposite ends of the outer race.
 17. The method of claim 15 includingspacing the plastics material from the inner race.
 18. A housing of anelectrical device, comprising: a housing body molded of plasticsmaterial; and a ground path of conductive material different than thatof said plastics material molded in place and embedded in said plasticsmaterial.
 19. A method of fabricating a plastics housing, comprising:molding a housing member in a mold to include a wall surface; removingthe molded housing member from the mold and, while the housing member isstill hot from the heat of molding, installing a separate piece in thehousing member adjacent the wall surface and permitting the housingmember to cool and to cause the wall surface to constrict about theseparate piece to secure the separate piece to the housing member.